I bet the AT fluid temp is reaching too high a temperature.
You might look into an aftermarket transmission cooler placed inline the AT cooler circuit after exiting the radiator.
Really any AT transmission could benefit from one if regularly used to tow in these conditions.

 

As far as I know there is not a way to put a transmission cooler on the cvt units as they are sealed units. If there is a way it would be great. However, if the tranny overheats in such a mild situation yhen it means SOA should throw out their 2700 towing limit or say if only works in the winter, or sell a tranny cooler such as I used have on my Pilot or Surburban.

 

Not so. The first thing I did was mount a hitch, trailer wiring and the most important piece the auxiliary transmission cooler. The two transmission lines for the stock cooler that is in the radiator are located on the driver's side subframe rail up front. You want the return line as the stock cooler will do the initial cooling then the auxiliary cooler does the rest. I know there is a thread buried on it here as I used it to help me locate which was the return line. If you are going to tow then an auxiliary cooler is a must. Also there has already been a thread posted on how to change the fluid in the CVT. I have not done it yet but will be soon. I am not a believer in lifetime fluid in anything mechanical where friction is involved.

 

Every transmission has a cooler even a cvt. Just need to get with a Subaru dealership or a good subaru mechanic to figure out a better solution.

 

I'd get to the dealer and bring up the issues. There might be a gremlin running around in your Subie. Since the seat belt light and the AT light seem to be acting in a sort of unison I'd suspect an electrical problem.

Have you towed this trailer before or was this the first time?

 

Don't use cruise going uphill.

 

There is a lower tow limit when going up long hills in hot weather. It is in the manual. I believe it is 1,250 pounds or so.

 

Ok so heres the scoop. CVT and AT. Both have cooling related limitations. CVT 1350lbs in 104+ temps abd long climbs. 5spd AT 1500lbs. Things that lower that rating box trailers and head winds and towing at high speed. MT do not have cooling issues in the same sense. Even the mt car will be pushing cooling limits in hot temps and 1500lbs steep climbs and high speeds.

Curious what rpms you were running on the climbs. I have towed enough in 80+ temps with a few good climbs never had a temp warning.

BTW little hint cvt cooling and engine cooling are tied together. Kick the heater on run the fan on high to shed some extra heat. Dont run over 3300 3400 rpm at the top end during the long climbs and you should be much better off.

#1 You will all ways run out of cooling before you run out of power when towing and decent climbs.

 

80-90f is warm but.... When towing with an automatic higher engine rpm's provide better transmission cooling. The Outback is not exactly a "tow" vehicle but probably will do better with manual (paddle shift) to 5th in this situation to provide better transmission fluid cooling through the trans. cooler. In my F-350 drw when carrying or towing a heavy load (has a trans. temp. guage) higher engine rpm's result in lower transmission temps. We obviously have no trans. temp gauge other than the overheat light in our o.b.'s. Downshift or go to manual and ease up a bit. 1500# up a long grade takes a lot of power, plus this is a little 4 banger that is meant to move the car not that and tow up a fricken hill/mtn. BTW: Elevation/altitude will also have a bearing on available h.p. that can be produced in a normally aspirated (non-turbocharged) engine, i.e. higher =less hp that can be produced!
Of course all that does not explain the air bag issue....don't you just love all the fancy smancy computer crap on cars these day's???? One blip here and a whole bunch a other blips show up for now apparent reason. :gasp::gasp:

 

+1 I haven't towed that much weight yet, but have noticed that on an upgrade with speed control engaged that the tach is fluctuating up and down a bit. This is the computer adjusting the CVT ratio up and down trying to maintain the best economy possible but also adjusting for the increased load. I have to believe this minor "hunting" or shifting the CVT ratio generates some heat in the transmission. When I'm towing my boat (1200#) on the freeway this summer I plan to go to manual mode 5th on the CVT to let the engine rev a little higher, stop the ratio fluctuations on the CVT, and hopefully keep both the engine and transmission a little cooler. Even on my V8 pick-up I lock out the overdrive whenever I'm towing more than 1000 lbs, and my Subie is just a 4 banger, so it just seems to make sense.

 

Wait, why would higher RPMs provide better cooling? after about 2000rpm you'll get the same flow rates through both water & ATF pumps, and the fans on outbacks are electric.

Now, I could see the higher RPMs of a lower gear equivalency producing somewhat less heat from the trans even though you are producing more heat from the engine - same fuel burn, more friction. Not like these cars have crank-driven fans.

...at the end of the day safe towing includes being able to handle any interstate grade at 40mph but if you want to go faster, bring more to the table or expect poorer results.

I'm still in overall agreement with patchelect that there may be an electrical issue at play.

 

Wait, why would higher RPMs provide better cooling? after about 2000rpm you'll get the same flow rates through both water & ATF pumps, and the fans on outbacks are electric.

Now, I could see the higher RPMs of a lower gear equivalency producing somewhat less heat from the trans even though you are producing more heat from the engine - same fuel burn, more friction. Not like these cars have crank-driven fans.

.

I am not sure how the transmission fluid is cooled on the OB, but on my truck it is cooled with a by a oil/transmission fluid heat exchanger so the water pump rate doesn't matter as long as the engine temps stay in range and the oil flow rate/temp stay in range. Big rig trucks running up hill are @ lower gear/higher rpm's for same reason. Maybe I'm not explaining well or am off the mark on this. I certainly agree that I would take it in for a computer read and??? I just don't think these little 4banger's are meant to tow at or near limit's without a need to adjust operating procedures.

 

Oh and yes the cvt has a cooling system. Sealed simply means no maint till 100k in non towing use. Doesn't mean the cvt lacks cooling for its fluid.

 

Shadetree -- with any AT CVT or other wise when your facing a long climb where temps could pose a challenge its always more efficient to manually pick a gear lock that gear down and simply do your climb based on RPM with your speed being more or less your secondary concern. This is what truckers do by the way. Any time AT's hunt or change gears during a long climb and towing they generate added heat. Not to mention its annoying to have an AT changing things up on you when you found the happy rpm and are just plugging along up the hill.

For those long climbs where you know that running temps with the AT are a very real possible problem. Your goal is to choose a gear that lets you run in an RPM range where you getting into the upper torque band of the power yet you want to keep to the lower end of those RPM's to keep heat generation on the exhaust and engine side of the program under control. RPM's are your friend till your generating far more heat and friction than whats needed to get the job done. The Flat 4 in the subaru is pretty cool regarding its flat torque curve. When grinding over a long climb running the car at 3200rpms is more or less giving you nearly as much pulling grunt as you get at 4000 yes you might be going a little faster but 4000rpm is generating way more exhaust heat and friction with the engine than 3200 is and your speed pending your climb and load maybe only 10mph faster if that.

Thats where you lock into a gear pick an RPM that lets you cruise along in the slow lane doing what 50-45mph if your trailer load and climb is really that steep and you just let the car do its thing. No temp issues and your car survives the trip. Even my 4.7L V8 has made some trips where a 1800lb trailer 110 degree heat had us doing 45mph up a 19 mile climb to 8000ft starting at just 850ft. We wanted AC on to stay comfy and doing 45-50mph up the climb was no big deal. I could have done 70mph but for sure the AC would have been off and we would have been cooking some expensive parts.

The Subaru CVT works great in AT mode but on those long hot climbs pick a gear 3rd - find the 3200rpm mark and plug along if you can carry 4th at 3200 then the speed bonus is great. Jump it to 3500-4000 for a speed boost to get around slow traffic if needed etc. But I found our CVT and 2.5 will grind along all day long at 3200rpm without heating things up on the really tough climbs. I've been down to 2nd at 3200rpm a few times it gets slow but hey if you wanted a fast tow you would have bought a F350 Diesel which would have towed that trailer at 90mph with the AC blasting with no indication of anything getting hot.

 

Gee thanks Professor! If you had taken the time to read my previous (1st) post you could've saved much of the lesson. BTW: I don't tow with my OB, I have a F350 dually with a turbo diesel for that. ha ha I was correcting my thought about the cvt being cooled with a oil/trans fluid heat exchanger which is common to most "regular" automatic transmissions. Other than that just passing on the Subie tech. comments. Your info about the rpm band is well taken.

 

I have actually done a number trips with this trailer before. Prior to this happening I pulled the trailer over the Tehachapi mountains at equal temperature and steeper hills when going from West to East.

In relation to not using cruise control: it actually should make no difference as the lineartronic transmission is basically choosing the rpm on the basis of the speed you ask it to go. In order to maintain 60 mph cruise will adjust the rpms, increasing them as needed to maintain that speed. It actually does not hunt but acts as if you were pressing the accelerator to maintain a constant speed. It appears to be a direct mathematical relationship. Higher rpms as hill steepens to maintain same speed.

Therefore if you slow down on a steep long hill that should actually reduce how hard the transmission works, whereas keeping it in a lower gear will necessitate it spinning higher rpms which unless there is a special cooling fan built in which comes on when excess heat builds up, the laws of physics require the transmission to produce more heat at higher rpms.

In actual practice I watch the cvt gradually downshift which produces higher rpms to match the steepness of the hill and this is done linearly so that it is already doing what some suggest but faster and more efficiently than I could.

I am interested in whether it is possible to install a tranny cooler. Does anyone really have an idea if this is possible? Would you not need an opening into the transmission for hot fluid to cone out, go through a heat exchanger to dissipate the heat and then flow back into the transmission? From previous readings I thought this was not possible with the Subaru had set up the the cvt.

Thanks everyone for the input. Again my 2006 MT Outback never had a problem pulling this exact same trailer in higher temps with two kayaks added at tomes, and let us not forget 1400 lbs. Is less only about 50% of what 2013 OB is rated to pull.

 

In actual practice I watch the cvt gradually downshift which produces higher
rpms to match the steepness of the hill and this is done linearly so that it is
already doing what some suggest but faster and more efficiently than I could.

Not so sure about the 'linearly' part. The power required to climb a given
grade at a given speed is dictated by aerodynamics, Isaac Newton, and
internal drivetrain losses. The first two are independent of rpm, while
drivetrain losses depend (in a highly nonlinear fashion) on both rpm and
throttle opening.

Bottom line: I wouldn't try to predict the optimum rpm/throttle opening
for a given grade and speed -- it depends ONLY on internal losses that
are probably/hopefully a small-ish fraction of the total power output.

...OTOH, it's easy to predict that slowing down is a guaranteed win-win,

Looby

 

your 2006 outback was not a cvt obviously.

 

No, my 2006 was a MT. I really appreciate the recommendations and it is making more sense to me now, especially the part about choosing a moderate rpm range as the priority and not worrying about maintaining a set speed. I have gotten used to letting the cvt cruise maintain speeds when not towing. Also my 2007 honda civic hybrid has spoiled me in cruise with its cvt and will run away from more powerful cars in the mountains in cruise.

I will have the fluid checked in the tranny in the OB when I get home and try the lower gear and slower speeds. Thanks again.

 

Anything beyond flat towing cruise control can get you into big trouble regarding the car trying to keep speed up when its working hard and heating things up.

The heat exchanger works pretty well till the engine its self is being run at such a level that the oil temp for the engine is just as hot or hotter than the AT fluid. Pretty much all engines have one major weak spot especially when towing a load in hot temps. Exhaust temps can get very high when your running the engine at high RPM's under a pretty good load. This heat can build up and start to impact engine cooling and due to the heat exchanger impact the AT cooling ability etc. Heat Exchangers can work both ways.

By knowing your engine power band regarding where the torque curve is compared to the RPM's you can manage the RPM's in the range you know the engine is generating good torque yet keep the RPM's at the lower end of the scale to help with exhaust heat and engine heat. This in turn helps with keeping the AT cool also due to the heat exchanger.

The CVT does a fantastic job managing gear ratios it will even settle down in a lower ratio when flat towing a trailer that is creating enough DRAG as Looby pointed Drag being a big impact on the towing ability the CVT doesn't blindly migrate to the highest cruising gear it does have some logic happening and will run a lower gear where the speed and throttle settings indicate that lower gear ratios are needed. The CVT may hunt a little but it seems to hunt far far less than my Toyota 5spd AT in my truck.

By choosing manual mode on a climb and picking 3rd or 4th or heck even 2nd if the climb is wicked enough going off cruise and accepting your going to be moving slower during the climb and by picking that sweet spot RPM for the climb your doing several things to help keep running temps under control.

Each trailer is a little different regarding drag - weight etc. So that RPM sweet spot takes a little experimenting. Also be aware that your temp lights there is a warning that things are getting hot and knowing how to help cool things off while on the move is pretty important. Keeping the RPM's under check, turning AC off and heat on with full fan not comfortable for passengers but that heater core sheds lots of heat when you need to help cool things off. Slowing down helps reduce wind drag even just 2-3mph drop in speed and if needed dropping another gear to keep the RPM's in that sweet spot can make a huge difference.

I've had to do this even flat towing in my old Land cruiser. Huge head wind 25+mph head wind and 110 degree temps dropping from 65mph to 61mph was the difference between raising the temps and the truck being perfectly happy. Cruise control was only an option if I kept a close eye on temps and dropped the speed manually when things started to show we were pushing it too hard.

 

An added cooler is not a bad idea. However I'm not sure where we would put it given the locations where we have space to do it could result in reducing the factory cooling ability or having no impact. Again heat exchange between two different cooling systems is possible and won't add cooling capacity it just moves heat from one system to another.

Given we have an exchanger on the AT. One Idea I've thought about off and on if I find that I need added cooling is to find a larger radiator more capacity - more cooling for the engine and this would help enable the heat exchanger for the AT to have a cooler engine to exchange heat with on the oil system. Could be far more effective than fooling with an added cooler on the AT end of the system. Though either one needs to be tested. You need before running temps under a specific load and outside temps so you have a base line of the stock system. Then do a cooling system change and see how the results are under the same loads and temps to see if running temps are more stable etc.

 

Along with slowing down a bit, and using a lower ratio with the flippers, turning off the air conditioning will help with not overheating the tranny.....(The hear exchanger is in front of the radiator.......Anything that keeps the radiator from cooling as much will give you a hotter tranny).

Opening the windows until you get to the top of the hill, where you can turn the air back on, will probably give you another 5mph without overheating.

 

Very true the heat exchanger for the AC compressor sits on the front of the primary radiator so any reduction in heat your exchanging with the primary radiator is a big help when your reaching the upper limits of the cooling systems. The AC compressor also puts a little drag on the engine too so shutting it off for a climb helps reduce load on the engine also.

 

Running at a higher RPM can have a cooling effect. This is due mainly to the water pump working harder. I used to work on a particular model of transverse engine FWD car. One of the procedures involved bringing the engine up to a particular temp range. We would have a laptop plugged into the diagnostic port while we drove to watch the temp (temp gauge in the cluster was essentially a dummy gauge). We quickly found that we HAD to dri e at lower RPMs to bring the temperature up. I figured that a lower gear (higher RPMs) would bring the coolant temp up, but it was just the opposite.

For clarification, I'm talking about the same speed and load... Just a different gear.

 

at lower rpms, the combustion charge lingers longer in the CC. (this is one problem with 'lugging' and engine.) Intake air and raw fuel also help with cooling.

 

Thought I needed to post this here also as this is the thread I started.

Non-OEM Torklift hidden hitch may invalidate Subie warranty??

Follow-up to checking the tranny oil as forum members suggested.

I had the tranny fluid checked at the local dealership after explaining the circumstances. The fluid was fine, but the tech told me that he had spoken to Subaru and they informed him that the fact that I had an aftermarket hitch, a Torklift Class 3 hidden hitch, that my Subaru warranty might no longer be valid, that we had to use a OEM hitch when we towed.

The dealership tech could not see how having a non OEM hitch could invalidate the warranty.

Not sure it the person the dealership tech spoke to at Subaru is correct, but thought others should check this out with Subaru.

 

the burden of proof would be on Subaru if there was an issue. That is, they would have to prove that you towed something outside the weight limits in the manual. Or perhaps the wiring or hardware used on the mount compromised the vehicle.

I wouldn't worry too much about it.

 

Does Subaru sell a class III hitch? I wonder if they are looking to protect themselves by disclaiming warranty service because the car has been modified to allow a heavier trailer to be attached to it than can be handled by the transmission.

I agree with one lucky, they'd still need to prove that you actually did an overweight tow.